The invention relates to video tape cassettes. More particularly, the invention relates to an improved video tape cassette having flangeless type tape winding cylindrical hubs.
Recently, there has been a tendency to miniaturize video tape systems while improvements in the performance of video tapes are concurrently desired. More specifically, recently the diameter of rotary drums for video tape devices have been reduced leading to a decrease in the size of the casings of video tape cassettes used with such systems. Miniaturization of the rotary drums and the cassette casings is essential for portable video systems.
In a conventional video tape cassette, the tape winding hubs are provided with flanges. The hubs are mounted at predetermined positions in the lower half of the cassette in advance during the assembly of the cassette. In order to prevent the removal of the hubs from the predetermined positions, ribs are provided on the inner surface of the lower cassette half at positions so as to surround the flanges of the hubs mounted at the predetermined positions.
Hubs with flange are disadvantageous in the following points. Since the flange must have a certain minimum thickness, the overall depth of the hub is relatively large. This is an obstacle to the miniaturization of the video tape cassette.
In order to realize a practical miniaturized video tape cassette, it has been proposed to use a flangeless cylindrical hub as the tape winding hub. A flangeless hub is thinner by as much as the thickness of the two flanges than the hub with flanges and, accordingly, the size of a video tape cassette with the flangeless hub can be made smaller.
However, the flangeless hub has certain disadvantages. In a conventional video tape cassette, in order to prevent rotation of the hubs, that is, in order to prevent slack in the tape when the cassette is not used, a tape slack preventing mechanism is provided which includes teeth formed on the periphery of the flange of the hub and a ratchet pawl pivotally mounted on the casing which can engage and disengage with the teeth. Since a flangeless hub has no flange, it is impossible to provide such a tape slack preventing mechanism as in a conventional cassette.
If the hub or reel is modified so that it has no flange as described above, then the space occupied by the reels can be reduced and accordingly the size of the cassette can be also reduced. However, another problem arises with such a modification relating to the absence of means for suitably controlling the magnetic tape wound on the reel. For instance, if the rotary shaft of the video is inclined, the magnetic tape while being run is shifted upwardly or downwardly with respect to the desired running direction as a result of which the tape is wound irregularly on the reel or hub. As a result, the end faces of the wound tape become parabolic or stepped and the magnetic tape is run unstably. This adversely affects the reproduced picture quality and lowers the overall reliability of the video system.